Evolution has a "work offline" mode - and it's easy to get into offline mode...
Take a look at the lower, left-hand part of the window in the status bar. If you see a little plug that's disconnected, click it to connect again. Alternately, you can go to the menu and click File -> Work Online. That does the same thing.
If this doesn't fix it, I'd be really surprised! Things like Airplane Mode might disable it automatically...
Obsidian Mini 9 >
2gb ram, 16gb ssd, bluetooth, 1.3mp webcam, us-intl kbd Internal Mods >
usb hub, 16gb flash drive, 8gb flash drive, added webcam, changed kbd Software Mods >
Dellbuntu 8.04.1 | Gentoo 2008.0